This invention relates to an arrangement for engaging a differential lock, and in particular to a mechanical arrangement for engaging the differential lock in the back axle of a vehicle such as an agricultural tractor.
Agricultural tractors are usually provided with a differential lock in the back axle for reasons well known to those skilled in the art.
One requirement of a differential lock arrangement for a tractor is that it can be easily engaged and disengaged. In fieldwork the driver must be able to engage the differential lock quickly when one drive wheel starts to spin faster than the other. Furthermore, tractors are required to make tight headland turns, and therefore it must be possible to disengage the differential lock quickly, otherwise the tractor driver will not be able to turn the vehicle and may crash into a hedge or ditch with possible disastrous consequences.
It is known to provide electro-hydraulic control systems, which engage and disengage the differential lock at the flick of a switch. In more complicated control systems sensors engage and disengage the differential lock automatically to ensure the optimum and safe performance of the tractor.
In many countries of the world there is not the requirement for, or the ability to maintain, complex electro-hydraulic control systems, and there is therefore a need to control engagement and disengagement of the differential lock mechanically. The present invention is concerned with mechanical arrangements for engaging and disengaging the differential lock.
In one known mechanical arrangement for controlling the engagement and disengagement of the differential lock a pedal is mounted on the tractor chassis. To engage the differential lock the tractor driver depresses the pedal with his foot. The tractor driver must keep his foot on the pedal whilst he wishes to have the differential lock engaged. When the driver removes his foot from the pedal the differential lock moves out of engagement.
When using a tractor for fieldwork, for example ploughing, engagement of the differential lock may be required most of the time. It would therefore be desirable to provide a mechanical differential lock engaging arrangement which does not require the driver to constantly depress a pedal whilst engagement of the differential lock is required.
EP292620 describes a differential lock pedal control system, which upon depression of the pedal, engages the differential lock. The differential lock is maintained in engagement by the control system when the driver removes his foot from the pedal. When the driver wishes to disengage the differential lock he depresses the pedal again, and the control system disengages the differential lock.
The pedal control system described in EP262620 comprises many parts, is complex, and expensive to manufacture.
It would therefore be desirable to provide a mechanical differential lock control arrangement which does not suffer from the problems associated with the prior art.
The invention provides a differential lock actuating arrangement comprising a pedal assembly including a substantially elongate member, mounting means to mount the said elongate member on the chassis of a vehicle, means to connect the said elongate member to a differential lock actuator, rotating means to rotate the said substantially elongate member about its longitudinal axis, wherein the mounting means mounts the said elongate member for movement between a first differential lock engaging position and a second differential lock disengaging position, and wherein the arrangement further comprises biasing means to hold the elongate member in one of the said first and second positions.
Preferably, the means to connect the said elongate member to the differential lock actuator comprises an over-centre cam mechanism. The over-centre cam mechanism may comprise a bracket fixed to the said substantially elongate member, and a linking member, wherein one end of the said linking member is pivotally attached to the differential lock actuator and the other end is pivotally attached to the said bracket.
Preferably, the mounting means includes a bracket comprising a slot, wherein the substantially elongate member is mounted in the said slot, and is permitted to move in the longitudinal direction of the slot, and wherein the biasing means is arranged to pull the elongate member towards the closed end of the slot. The biasing means may be attachable to the bracket and the substantially elongate member. The substantially elongate member may be provided with stops, which co-operate with the bracket to limit movement of the substantially elongate member in its longitudinal direction.
The rotating means may comprise a lever extending to either side of the longitudinal axis of the said substantially elongate member, and preferably, the lever is provided with engagement members, wherein upon exertion of pressure on one of the engagement members, the substantially elongate member is caused to rotate. Advantageously, the engagement members each comprise a pedal.
The invention also provides a tractor comprising a differential lock actuating arrangement as described.